Lubricant compositions



Elite This invention relates to novel lubricant compositions and a method for their use in lubricating rubbing surfaces. More particularly, the invention is concerned with the use of organo-metallic additives to enhance the lubricating properties of silicone oils and greases.

The term silicone as used in the specification and claims of this application is defined as a synthetic compound containing silicon and organic groups. In naming specific compounds, the nomenclature system recommended by the American Chemical Society Committee on Nomenclature, Spelling, and Pronunciation (Chem. Eng. News, 24, 1233 (1946) with be used. Thus, the compounds which have the linkages are the siloxanes. Derivatives of silane, SiH in which one or more of the hydrogens in silane are replaced with organic groups are termed the silanes. Silicates and silicate ester compounds are named as oxy derivatives of silane and are called alkoxy or aryloxy silanes.

Silicone oils are well known to have a high degree of thermal stability such that they are highly resistant to oxidation and thermal degradation in use at high temperatures. Their viscosity index is high and thus silicone oils and greases change relatively little in flow properties over a wide temperature range. In spite of these desirable characteristics, however, the widespread adoption of silicone oils has been hampered because they have one serious drawback, namely, their relatively poor lubricity as compared with that of conventional hydrocarbon oils. Because of their poor lubricity, they have not been found to be effective lubricants for a wide range of applications.

The lubrication of rubbing systems which operate at extreme pressures presents unusual lubrication problems since the lubricant film between the rubbing surfaces is subjected to high shear forces. Because of these high shear forces, the lubricant films which, under low pressure operating conditions, are present upon the surfaces of the rubbing members, are forced from between the rubbing surfaces so that effective lubrication is not obtained. In order to combat these problems accompanying extreme pressure conditions, it has been the practice of the prior art to utilize lubricant additives which corrode the rubbing surfaces so as to form a film on the surfaces which, in itself, acts as a lubricant. Such additives are spoken of as E.P. additives.

A typical example of such an El. additive is carbon tetrachloride which breaks down in a lubrication system to form degradation products that react with the iron oxide coating on a ferrous rubbing member to form a film of ferrous chloride which acts to lubricate the rubbing metal surfaces. Since the lubrication mechanism of BF. additives involves corrosion of the rubbing members, these additives have no lubricating effect in rubbing systems in which the rubbing members have non-reactive surfaces which resist corrosion by the additive. Typical examples of such non-reactive rubbing systems are titaninm-on-titanium, stainless steel-on-stainless steel, and goldon-gold. The non-reactivity of the rubbing surfaces may be due to the resistance to corrosion of the material forming the rubbing members as is the case of gold rubbing on gold wherein the gold is essentially inert to any chemical reaction. Further, it may be due to the non-reactivity 3,@58,9l2 Patented Oct. 16, 1962 of an oxide film which is present on the surfaces of the rubbing members as in the case of titanium'on-titanium, since titanium readily forms a surface oxide coating which is extremely non-reactive. An example of a non-metallic rubbing system in which the rubbing members are nonresponsive to ER additives is nylon rubbing on nylon, since the nylon is substantially chemically inert. Other plastics which cannot be lubricated by HP. lubricant additives are the polymethyl methacrylates, polyvinyl chloride and polyethylene.

It is, therefore, a general object of this invention to provide silicone lubricants, both greases and oils, with improved lubricity characteristics. A more particular obiect of this invention is to provide silicone lubricant compositions which are efiicacious in lubricating rubbing systems operating under severe conditions in which the rubbing surfaces are non-corrodible by conventional E.P. additives. Another and more particular object is the provision of a method for utilizing improved silicone lubricants in lubricating metal rubbing surfaces under extreme pressure conditions. Additional objects of the invention will become apparent from the description and claims which follow.

In the accomplishment of the above Objects, it has been found that the lubricity of silicone base lubricants may be greatly enhanced by adding thereto an organometallic compound in a quantity sufficient to increase the lubricity of the silicone base lubricant. Although the invention is not limited to any particular mechanism of anti-wear action, it is believed that a film is formed on the rubbing surfaces, said film being formed substantially entirely from the degradation of the organometallic additive under the influence of heat and pressure generated at the contact points of the rubbing surfaces. Thus, the film is formed independently of any corrosive mechanism as required in the case of conventional E.P. additives and, accordingly, the film is efiective in lubricating surfaces which are essentially non-reactive and have a high resistance to corrosion.

The organometallic additive can be present in the silicone lubricant in various concentrations and in various forms of dispersion. In the case of a silicone grease, the organometallic additive may be present in the form of well-dispersed, finely-divided particles, whereas in the case of a silicone oil, it is preferable that the organo-.

metallic additive be soluble in the oil so as to form a solution. In principle, the higher the concentration of the organometallic additive in the silicone lubricant, the greater is the lubricating power of the product obtained. Experience has shown, however, that very low concentrations of the order of 0.1 percent by weight of the organometallic additive in the silicone lubricant increase its lubricity. In view of the high cost of organometallic compounds. generally there is an economic limit to their concentration in the base silicone, a limit which could be fixed at about 10 percent by weight in the present state of economic conditions. Moreover, when the concentration of the organometallic additive is increased to above 10 percent, the physical properties, for example, viscosity, of the resulting composition may be quite different from those of the silicone base so that the desirable physical properties of the silicone base fluid may be markedly changed. In fact, with extremely high concentrations of the organometallic additive, a situation can be reached in which the silicone lubricant is in effect the additive and the organometallc compound is the base fluid since the physical properties of the resulting composition are more like those of the organometallic component than like the silicone component. Thus, the preferred composition range of the invention ranges from 0.1 to 10 percent by weight of the organometallic additive in the silicone lubricant.

suited for use The organometallic compounds employed as additives to silicone base lubricants Within the scope of the present invention are compounds of the metals in groups IIIA and IVA of the periodic table as found on pages 58 and 59, Langes Handbook of Chemistry, published by Handbook Publishers, Inc., Sandusky, Ohio, 1949. More specifically, the additives may include compounds of aluminum, gallium, indium, thallium, lead, tin, and germanium. Not

included are the compounds of boron and silicon, since these elements are primarily non-metallic.

The organometallic compounds utilized in this invention may be further characterized as compounds in which there are monovalent carbon-to-metal bonds in the molecule. Typical examples are the metal alkyls, such as tetraethyllead, dimethylethyl aluminum, trieicosyl thallium, tridecyl indium, and tetrapentadecyl germanium; the metal aryls, such as tetraphenyllead, tri-(4-methylphenyl) aluminum, and tetra-(4-isopropylphenyl) tin, and the metal alicyclic compounds, such as tricyclohexyl gallium and di-(2-ethylcyclopentyl) dicyclohexyllead.

The organic radical bonded to the metal may be unsaturated as, for example, in tetra-(Z-propenyl) lead, tri- (1,3-butadienyl) aluminum, cyclopentadienyl tricyclohexadienyl tin, and the like. Further included are compounds in which the metal atom is bonded to mixed hydrocarbon groups, such as dimethyldiphenyllead, tricyclohexylmethyl tin, di-(2,4-cyclohexadienyl) cyclopentadienyl indium, methylethylcyclohexyl-Z-propenyl lead.

Based on a number of considerations, certain of the organometallic compounds of the metals of groups IIIA and IVA have been found more suitable as lubricant additives to silicone fluids than have other of the aforesaid organometallic compounds. In terms of availability and cost, the organometallic compounds of aluminum, tin and lead are preferred since these metals are readily available and of relatively low cost. In terms of oxidative stability the organometallic compounds of gallium and aluminum are less stable than are the organometallic compounds of the other metals of groups IIIA and IVA. Thus, the aluminum and gallium compounds are better as additives to silicone base fluids at low concentrations, whereas the organometallic compounds of the other metals of groups IIIA and IVA may be utilized more readily over a wide concentration range. The considerations based on the oxidative stability of the organometallic compounds are of lesser importance when the lubricant compositions are used in a system from which oxygen is excluded. Generally, the aryl-substituted organometallic compounds have been found to be more thermally stable than are the alky alkenyl-, and cycloalkyl-substituted metal compounds. Thus, for high temperature applications, the aryl-substituted organometallic compounds are found to be the most effective additives to the silicone base fluids.

In terms of all of the considerations set forth in the preceding paragraph, the organometallic compounds of tin and lead are the preferred silicone lubricant additives. These compounds are generally oxidatively stable and readily available at a reasonable cost. The compounds having branched chain hydrocarbon substituent groups are generally more unstable than .are their straight chain counterparts and thus straight chain substitution is generally found to produce a better silicone lubricant additive.

Since the solubility of the organometallic compounds in silicone oils and greases generally decreases as the number of carbon atoms per molecule is increased, a preferred class of organometallic compounds for use as silicone additives is represented by the organometallic compounds of the metals of groups IIIA and IVA wherein each molecule contains from 2 to 35 carbon atoms. It has been found that the compounds within this range are soluble in silicone oils to the extent required to form an effective lubricant film on the surfaces of the rubbing members during use of the lubricant. At the same time,

because of the solubility of the preferred organometallic compounds in silicone oils, the concentration of the organometallic compound is uniform throughout the lubricant and forms a stable composition which remains constant over extended periods of time during shipment and storage. Solubility of the organometallic component in the silicone base is not so important when the silicone base material is highly viscous as is the case with silicone greases, since the organometallic compound may then be incorporated in the grease in the form of finely-divided dispersed particles.

The organometallic compounds used in the lubricant compositions of the invention may be halogen substituted, may contain sulfur in the molecule, or may contain varions functional groups such as the carbonyl and the carboxyl group. Examples of such compounds are triethyllead chloride, dimethyl indium bromide, di-n-butyl tin sulfide, ethyl indium sulfide, cyclohexyl thallium sulfide, diphenyl germanium sulfide, tricyclohexyl tin fluoride, and di-n-butyl tin dilaurate.

Methods for the preparation of the organometallic compounds used in formulating the lubricant compositions of the invention are set forth in Die Chemie der metall-organischen Verbindungen by Drs. Krause and Von Grosse. The book was produced in the form of a Photo-Lithoprint Reproduction by Edwards Brothers, Inc., of Ann Arbor, Michigan, in 1943, under the authority of the Alien Property Custodian, License No. A245.

The silicone oils and greases serving as the base medium for the lubricant compositions of the invention include the polysiloxane oils and greases of the type, poly- .alkyl-, polyaryl-, polyalkoxy-, and polyaryloxy-, such as polydimethyl siloxane, polymethylphenyl siloxane, and polymethoxyphenoxy siloxane. Further included are silicate ester oils, such as tetraalkyloxy and tetraaryloxy silanes of the tetra-Z-ethylhexyl and tetra-p-tert-butylphenyl types, and the silanes. Also included are the halogen-substituted siloxanes, such as the chlorophenylpolysiloxanes.

The polyalkyl, polyaryLand polyalkyl polyaryl siloxanes are the preferred types of base medium for the lubricant compositions of the invention because of their high oxidative stability over a Wide temperature range. The polyalkyl siloxanes, such as the dimethyl polysiloxane, are slightly preferred over the polyaryl, and polyalkyl polyaryl siloxanes because they show the least change in viscosity over a Wide temperature range.

The silicone base lubricants of the invention are far superior to mineral oil base lubricants because of their greater oxidative stability and their high viscosity index.

As a further illustration of the invention, the following examples show typical lubricant compositions Within the scope of the present invention. Unless otherwise specified, proportions given in these examples are on a Weight basis.

EXAMPLE I Five'parts of tetraethyllead were blended with parts of Dow-Corning 200 silicone fluid. Dow-Corning 200 silicone fluid is a dimethyl polysiloxane having a viscosity of centistokes at 25 C., an open cup flash point of 575 F. (ASTM D92-33), a pour point of -67 F. (ASTM D-97-39, Sections 5 through 7), a specific gravity of 0.970 at 77 F., and a thermal conductivity of 0.00037 g1n.-cal./second/centimeter C. differential/ one centimeter thickness.

EXAMPLE II EXAMPLE III Five parts of di-n-butyl tin sulfid were blended with One-tenth part of tetramethyllead is blended with 99.9

parts of a phenylmethyl olysiloxane of high phenyl content. The fluid is Dow-Corning 710 silicone fluid, having a viscosity of 475-525 centistokes at 25 C., an open cup flash point of 575 F. (ASTM D-92-33), a freezing point of -8 E, and a specific gravity of 1.10 at 77 F.

EXAMPLE V One part of trieicosyl thallium is blended with 99 parts of the phenylmethyl polysiloxane fluid described in EX- ample IV.

EXAMPLE VI Pour parts of tetra-(4-isopropylphenyl) tin are blended with 96 parts of a dimethyl polysiloxane fluid. The fluid used is Dow-Corning 200 silicone fluid having a viscosity of 500 centistokes at 25 C., an open cup flash point of 600 F. (ASTM D9233), a pour point of 58 F. (ASTM D97-39, Sections 5 through 7), and a specific gravity of 0.972 at 77 F.

EXAMPLE VII Eight parts of di-(2,4-cyclohexyl) cyclopent-adienyl indium are mixed with 92 parts of the silicone grease used in Example VII.

EXAMPLE IX Ten parts of tetraisopropyllead are blended with the polyalkyl siloxane fluid described in Example I.

EXAMPLE X Three parts of tricyclohexyl gallium are blended with 97 parts of -a phenylrnethyl polysiloxane fluid. The silicone fluid used is Dow-Corning 550 fluid having a viscosity of 100-150 centistokes at 25 C., an open cup flash point of 575 F. (ASTM D9233), a freezing point of -60 F., and a specific gravity of 1.07 at 77 F.

EXAMPLE XI Five parts of ethyl aluminum sulfide are blended with 95 parts of a polyalkyl siloxane fluid as described in Example VI.

EXAMPLE XII Seven parts of trimethyl indium are blended with 93 parts of a silicate ester oil. The silicate ester oil is monoethyl diethoxy monoacetoxy silane, which is a liquid having a boiling point of 191.5 C.

EXAMPLE XIII Two parts of tri-(1,3-butadienyl) aluminum are blended with 98 parts of tribenzyl-n-hexadecyl silane which is a liquid having a boiling point of 245248 C.

EXAMPLE XIV Four parts of diphenyl germanium sulfide are mixed with 96 parts of a halogen-substituted polyphenyl polymethyl siioxane. The siloxane fluid is Dow-Corning "F- 60 fluid having a viscosity of 71 centistokes at 25 C. and 24 centistokes at 75 C., a specific gravity of 1.03 at 25 C., a freezing point of -70 C., and a flash point of 540 F.

EXAMPLE XV Five parts of di-n-butyl tin sulfide were blended with parts of Dow-Corning F-60 fluid having the physical characteristics set forth in Example XIV.

EXAMPLE XVI Five parts of tetraethyllead were blended with 95 parts of Dow-Corning 710 silicone fluid having the physical characteristics set forth in Example IV.

Numerous lubricant compositions containing a silicone oil or grease and an organometallic compound as defined above were tested in a four-ball lubricant test machine to determine the lubricity of the respective lubricant compositions relative to a baseline of neat silicone oil or grease. Two types of four ball lubricant test machines were used in these tests. They were the extreme pressure lubricant tester (hereinafter referred to as the E. P. tester) and the four-ball wear machine. The E. P. tester is described by Boerlage in Engineering, vol. 136, July 14, 1933, pp. 46-47. The four-ball wear machine is described by Larsen and Perry in the Transactions of th A.S.M.E., January 1945, pp. 45-50.

The two types of four-ball lubricant test machines are essentially the same in principle of operation and difler only in their respective load ranges. The E. P. tester operates in the range of 10 to 800 kilograms and the four-ball wear machine operates in the load range of from 0.1 to 50 kilograms. The four-ball wear machine further differs from the E. P. tester in that it is more sensitive and can measure loads to a tenth of a kilogram, whereas the E. P. tester is not accurate in measuring load increments of less than one kilogram.

Both types of tour-ball lubricant wear machines utilize four balls of equal size arranged in a tetrahedral formation. The bottom three balls are held in a non-rotatable fixture which is essentially a universal chuck that holds the balls in abutting relation to each other. Since the bottom three balls are of equal size, their centers from the apices of an equilateral triangle. The top ball is affixed to a rotatable spindle whose axis is positioned perpendicularly to the plane of the ball holder and in line with the center point of the triangle whose apices are the centers of the three bottom stationary bails.

In operation, the four balls are immersed in the lubri cant composition to be tested and the fixture holding the three bottom balls is moved upwardly so as to bring the three fixed lower balls into engagement with the upper rotating ball. As the load is increased, the fixture is moved upwardly and axially of the rotating spindle afiixed to the upper ball.

The lubricity of the lubricant under test is determined by the amount of wear occurring on the lower balls at the points of contact with the upper rotating ball. If the lubricant is completely effective, the amount of wear will be negligible. On the other hand, if the lubricant is not completely eflective under the test conditions, the upper ball may weld or seize to the lower balls due to the heat of friction at the contact points or the wear which occurs will be excessive. If seizure does not occur, the average diameter of the circular scar areas of the lower balls is measured so as to give a quantitative basis for comparing the test results with those of other tests. As the severity of the test conditions is increased with a given lubricant composition, the likelihood of excessive wear of the lower balls is increased.

The results of a series of lubricant tests conducted in the four-ball wear machine are set forth in Table I. In these tests the upper ball was rotated at a speed of 572 r.p.m., the ambient temperature was 50 C., and the duration of each test was two hours. The balls were onehalf inch in diameter and constructed of SAE 52-100 steel.

Table I Load Average Scar Lubricant Composition Applied, Diameter on Lower Kilograms Balls, Millimeters Neat Dow-Corning 200 Silicone Fluid (see Example I) 5 0.47. Do 10 0.53. D 20 0.73. Composition of Example I. 0.35. Do 0.37. D0 0.45.

Neat Dow-Corning F-60 Silicone Fluid (see Example XIV). 2. 5 0.38. O 5 0.43.

40 0.97 (after 18 minutes-seized shortly thereafter).

Composition of Example XV 2. 5 019. Do 5 0.22. D0 40 0.76. Neat Dow-Corn 2 (see Example IV). 2. 5 0.87. D0 10 1.44. Composition of Example XVI 2. 5 0.30. Do 10 0.52.

The results set forth in Table I clearly show the eflectiveness of the lubricant compositions of the invention over that obtained with the corresponding neat silicone fluid.

Thus, the firs-t six tests set forth in the table illustrate the superiority of the composition of Example I containing five parts of tetraethyllead in 95 parts of Dow-Corning 200 silicone fluid over the neat Dow-Corning 200 silicone fluid. As shown, the composition of Example I is superior to the neat silicone fluid over the load range of from 5 to 20 kilograms, and is more markedly superior at the 20 kilogram loading than at the lower loads. The next six test results set forth in the table illustrate the superiority of the composition of Example XV containing five parts of di-n-butyl tin sulfide in 95 parts of Dow-Corning F-60 fluid over the heat Dow-Corning F-60 fluid. As shown, the composition of Example XV is superior to the neat F-60 fluid at the low loads of 2.5 and 5 kilograms and also at the high load of 40 kilograms. The next four test results set forth in Table I illustrate the great superiority of the composition of Example XVI containing five parts of tetraethyllead in 95 parts of Dow-Corning 7'10 silicone fluid over the neat Dow-Corning 710 fluid. As shown, the composition of Example XVI is a much more effective lubricant than the neat 710 fluid in that the average scar diameter produced when utilizing the composition of Example XVI as the lubricant is in the order of one-third the scar diameter produced when using the neat Dow- Corning 710 silicone fluid. The results of Table I show that the lubricant composition of the invention, covering a wide range of silicone base fluids, admixed with an 6 organometallic compound produce more effective lubrication over a Wide range of loading than do the neat silicone fluids.

A second series of tests was conducted in the four? ball wear machine and the results of these tests are set .forth in Table H. The four balls used'in these tests were made of steel and were uniformly coated with a 0.00l-inch thickness of pure gold. The speed of IO- tation of the upper balls was 79 r.p.m. and the tests were conducted at an ambient temperature of 50 C. Failure in these tests was manifested by a wearing through or stripping off of the gold plate accompanied by a sudden rise in the coe cient of friction to a high value and a production of massive particles of wear debris. Such failure is denoted in Table II as seized.

8 Table II Load Scar Diameter Lubricant Composition Applied, Length of on Lower Kilo- Run Balls, Milligrams meters Neat Dow-Coming 200 Fluid 0. 5 0.3 min..-- Seized.

(see Example I).

Do 1.0 0.25 min... Do. Composition of Example I 1. 0 2 hr Not measured. Five parts of tetramethyllead 1. 0 2 hr 0.48.

in parts or the Dow-CorniIug 200 fluid used in Example Five parts of tetraisopropyllead 1. 0 2 hr 0.46.

in 95 parts of the Dow-Cornmg 200 fluid used in Example Neat Dow-Coming 710 fluid 1. 0 2 hr 0.78.

(see Example XIV).

Composition of Example XVI-- 1. 0 2 hr 0.40.

Neat Dow-Corning F-60 fluid 1. 0 10 sec-.- Seized.

(See Example XIV).

Five parts of tetraethyllead in 1.0 2 hr 0.38.

95 parts of Dow-Corning F-60 fluid.

Composition of Example XV.-- 1. 0 2 hr 0.43.

The results set forth in Table II clearly demonstrate the effectiveness of the lubricants of the invention in increasing the lubricity of the silicone base fluids. Due to the chemical inertness of the gold surface on the four balls, this rubbing system is clearly unaffected by conventional E.P. additives and thus affords a good basis for demonstrating the superiority of the lubricant compositions of the invention.

The results of the first five tests as set forth in Table II demonstrate the marked eflectiveness of the lubricant compositions of the invention composed respectively of five parts of tetraethyllead in 95 parts of Dow-Corning 200 fluid, five parts of tetramethyllead in 95 parts of Dow-Corning 200 fluid, and five parts of tetraisopropyllead in 95 parts of Dow-Corning 200 fluid over that o obtained by the neat Dow-Corning 200 fluid. As shown in the first two tests, the neat Dow-Corning 200 fluid was completely ineifective in lubricating the gold-plated balls at loads of 0.5 and l kilogram. In contrast, the lubricant compositions of the invention as set forth in the succeeding three tests provided eflective lubrication at one-kilogram loads for periods of two hours. The next two test results set forth in the table illustrate the superiority in lubricating effectiveness of the composition of Example XVI, containing five parts of tetraethyllead in 95 parts of Dow-Corning 710 silicone fluid over that obtained by use 0 fthe neat DoWCorning 710 fluid. The scar diameter produced when using the composition of Example XVI was in the order of one-half the scar diameter produced under the same test conditions when using the neat Dow-Corning 710 fluid. Thus, in terms of scar diameter, the lubricant composition of Example XVI can be said to be twice as effective as the neat Dow-Corning 710 fluid. The succeeding three test results set forth in Table II illustrate the superiority of lubricant compositions of the invention containing respectively five parts of tetraethyllead in 95 parts of Dow- Corning F-60 fluid and five parts of di-n outyl tin sulfide in 9.5 parts of Dow-Corning F 60 fluid over the neat Dow-Corning F-60 fluid. The neat Dow-Corning F-60 fluid proved completely ineffective as a lubricant of the gold-plated balls of loads of one kilogram, since the balls seized in less than 10 seconds at this loading. In contrast, the lubricant compositions of the invention utilizing as the base silicone lubricant the Dow-Corning 60 fluid provided eifective lubrication of the goldplated balls for periods of two hours at loads of one kilogram.

A further series of lubricant tests were conducted in the ER tester as set forth in Table III. The four balls utilized were one-half inch in diameter and were made of 52-100 steel. The upper ball was rotated at a speed Tabfe III Load Applied, Kilograms Average Scar Diameter on Lower Balls in Millimeters Lubricant Composition Failed in less than one minute (weld) Neat Dow-Corning 200 Fluid (see 1'1):-

anliple I).

Composition of Example II Neat Dow-Corning 44 Silicone Grease (sefi Example VII).

3.37. Failed hi less than one minute (weld) 3. Failed in less than one minute (weld).

.As shown by the results of the first three tests, set forth in Table III, the composition of Example II, comprising five parts of tetraphenyllead in 95 parts of Dow-Corning 200 silicone fluid is a much more effective lubricant than the neat Dow-Corning 200 fluid. The composition of Example II provided effective lubrication at loads of 130 kilograms, whereas the neat Dow-Corning 200 fluid was not eifective at loads in excess of 100 kilograms. Further, the scar diameter resulting from the tests utilizing the composition of Example II were far less than the scar diameter produced when utilizing the neat Dow-Corning 200 fluid at a load of 100 kilograms. The test results set forth in the remainder of Table III illustrate the great superiority of the composition of Example VII, containing five parts of tetraphenyllead in 95 parts of Dow-Corning 44 silicone grease, over the neat Dow-Corning 44 silicone grease. As shown, the composition of Example VII not only enables effective lubrication at a much higher load than that found possible with the Dow-Corning 44 silicone grease, but also provides more effective lubrication over the entire loading range of from 40 through 100 kilograms as illustrated by the much smaller scar diameter produced in the tests using the composition of Example VII as compared with the scar diameter produced when using the neat Dow-Corning 44 silicone grease. The results set forth in Table III clearly demonstrate the effectiveness of my lubricant composition at loads in excess of 100 kilograms when utilizing either a silicone oil or a silicone grease as the primary constituent of the lubricant composition.

In utilizing the lubricant compositions of the invention, it has been found that their lubricating effectiveness can be greatly increased by a proper running-in of the lubricant composition in the test machine. The running-in comprises using al oad between the rubbing surfaces that is initially low and isg radually increased up to the operating load. As a result of this gradual increase, the lubricant composition is effective at high loads which would, in the absence of a running-in period, result in instantaneous failure.

The beneficial effects of a runningin period are illustrated by way of the following examples of tests conducted in the four-ball wear machine. The four balls in each of the tests were plated with a gold coating having a thickness of 0.001 inch, the speed of rotation of the upper ball was 79 rpm, and the temperature at which the tests were conducted was 50 C.

EXAMPLE XVII The lubricant composition of Example I containing five parts of tetraethyllead and 95 parts of Dow-Corning 200 silicone fluid was run in the four-ball wear machine at a load of five kilograms. Failure occurred instantaneously.

l 0 EXAMPLE The lubricant composition comprising 10 parts of tetraethyllead and parts of Dow-Corning 200 silicone fluid having the physical characteristics set forth in Example I was run in the four-ball wear machine at a load of five kilograms. Failure occurred instantaneously.

EXAMPLE XIX The lubricant composition of Example I was run in the four-ball wear machine for 120 minutes at a load of one kilogram whereupon the machine was stopped. The machine was then started and run for 2 /2 minute intervals at loads of 2.5, 5.0 and 10 kilograms, respectively. Following the 2 /2 minute run at 10 kilograms, the load was increased to 15 kilograms and run successfully for a period of 19 seconds, at which time failure occurred.

EXAMPLE XX The lubricant composition of Example I was run in the four-ball Wear machine for 2% minute intervals at loads of 0.5, 1.0, and 2.5 kilograms, respectively. I he load was then increased to 5.0 kilograms. The test was run for 122.5 minutes at this load, whereupon the load-was increased to 10 kilograms and run for 2 /2 minutes at this load. The load was then increased to 20 kilograms and run successfully for seven seconds at which time failure occurred.

The remarkable effect of a running-in procedure on the lubricating effectiveness of my lubricant compositions can be seen by comparing the results of Example XIX and XX with those of Example XVII. :In all three of these examples, the test lubricant utilized was the same and as set forth in Example -I, comprised five parts of tetraethyllead, blended with parts of Dow-Corning 200 silicone fluid. \As shown by the three examples, the use of a running-in procedure made possible effective lubrication at loads in excess of 10 kilograms, whereas use of the same lubricant compositions at loads of five kilograms without running-in resulted in instantaneous failure. Thus, the use of a running-in resulted in instantaneous failure. Thus, the use of a running-in procedure can be seen to have resulted in more than a percent increase in the lubricating effectiveness of the composition of Example I. Example XVIII serves to illustrate that the use of a running-in procedure as in Examples XIX and XX provides more effective lubrication than can be obtained by using a larger percentage, 10 percent as in Example XVIII, of an organometallic compound in the silicone base fluid.

Similar beneficial results to those set forth above were obtained when utilizing a run-in procedure with other lubricant compositions of the invention. :The test conditions under which these runs were performed were the same as utilized in Examples XVII through XX, namely, gold plating of 0.001-inch thickness on the four balls, a speed of rotation of 79 rpm. of the upper ball and test temperatures of 50 C. A composition comprising five parts of tetraethyllead and 95 parts of Dow-Corning 710 fluid was run for 122 /2 minutes at a 1.0 kilogram load,

and for periods of 2 /2 minutes at loads of 2.5 and 5 kilograms. The lubricant was run successfully for eight seconds at 10 kilograms when failure occurred. A composition comprising five parts of tetraethyllead and 95 parts of Dow-Corning 1 -60 fluid was run for 122 /2 minutes at a 1.0 kilogram load, 2 /2 minutes at 2.5 kilograms, 2 /2 minutes at 5 kilograms, and failed after being run successfully for six seconds at 10 kilograms. A composition comprising five parts of di-n-butyl tin sulfide in 95 parts of Dow-Corning F-60 fluid was run for 122 /2 minutes at 1.0 kilogram, 2 /2 minutes at 2.5 kilograms, and failed after running successfully for 10 seconds at 5 kilograms.

An alternative mode of running-in involves the utilization of a lubricant comprising an organometallic in mineral oil or a synthetic lubricant other than the lubricants of this invention as the initial lubricant. Following a brief period of operation with this lubricant, the machine is stopped, the lubricant is drained out and replaced with a lubricant composition of the invention, namely, one containing a major proportion of silicone oil having admixed therewith an organometallic compound in which the metal is selected from groups IIIA or IVA and there is a carbon-to-metal bond in the molecule. The test is then run to completion with the silicone base lubricant composition.

A further ramification of the running-in procedure involves both the utilization of an initial run-in lubricant and the use of an initial low loading which is later increased up to the operating load at which the test is to be conducted. An illustration of this procedure is set forth in the following example.

EXAMPLE XXI A solution of five parts of tetraethyllead admixed with 95 parts of mineral oil was run in the four-ball wear machine for a period of thirty minutes at a load of five kilograms. The machine was then stopped and the lubricant was drained off and replaced with the lubricant composition of Example I, containing five parts of tetraethyllead and 95 parts of Dow-Corning 200 silicone fluid. The machine was started and run for 120 minutes at a load of five kilograms. The load was then increased to kilograms and the test was run for 2 /2 minutes, whereupon the load was increased to kilograms and run to failure. Failure occurred after 20 seconds at the 20 kilogram load. This test utilized one-half inch steel balls having a 0.00l-inch thickness of gold plate thereon. The upper ball was rotated at a speed of 79 r.p.m. and the test was conducted at 50 C.

A comparison of the results of Example XXI with those obtained in Examples XVII-XX shows that the effectiveness of the alternative running-in procedure utilizing an initial run-in lubricant is equally as effective as the run-in procedure of Examples XIX and XX. Such effectiveness results in a more than 100 percent increase in the lubricating effectiveness of the silicone base lubricant over that obtained when using the lubricant without a running-in procedure as in Examples XVII and XVIII.

The alternative mode of running-in as set forth in Example XXI is likewise applicable to the other lubricant compositions of the invention comprising an organometallic compound admixed with a silicone oil or grease. The initial lubricant used in the running-in can be composed of the organometallic compounds of the metals of groups IHA and IVA admixed with mineral oil or synthetic lubricants, such as those typified above.

The many examples and tables of test data and lubricant compositions set forth in the preceding portions of this specification are by way of illustration only and should not be construed as in any way limiting the scope of my invention. Obvious variations Within the scope of the invention will be readily apparent to one skilled in the art, such as, for example, using a plurality of the organometallic compounds of the metals of groups IHA and IVA as additives to a single silicone base lubricant, or in varying the time, load, and initial run-in lubricant composition from those set forth in the examples of this specification illustrating run-in procedure.

The lubricant compositions of my invention may also contain other compounds, such as soaps, antioxidants, thickeners, or other additives which are present in commercial silicone lubricants, since such additives in no way inhibit the effectiveness of the lubricant compositions of the invention. The lubricant compositions of my invention are not restricted to use with any particular rubbing system, metal or non-metal, since their mechanism 12 of operation is effective in lubricating any combination of rubbing surfaces. Their greatest utility, however, is found in lubricating chemically inactive rubbing surfaces since it is in this area that conventional E.P. additives are ineffective.

A further utility of the lubricant compositions of the invention is in lubricating electrically conductive noble metal rubbing systems, such as, for example, the silver-silver or silver-graphite contacts found in electrical switches, relays, motors, and electrical generating equipment. The lubricant films laid down by many of the lubricant compositions of the invention have high electrical conductivity and, therefore, would not inhibit the transfer of electrical current between the rubbing members.

Having set forth and described the invention fully by way of the preceding examples and explanation, I desire to be limited only by the scope of the following claims which define my invention.

I claim:

1. Composition of matter consisting essentially of a silicone base lubricant and an organometallic compound of a group IHA-IVA metal having a carbon-to-metal bond in the molecule, said compound containing from 2 to 35 carbon atoms per molecule and being present in a quantity sufiicient to increase the lubricity of the silicone base lubricant.

2. The composition of claim 1 wherein the organometallic compound is selected from the group consisting of organolead compounds and organotin compounds.

3. A method for lubricating rubbing surfaces with a lubricant consisting essentially of a silicone base lubricant containing a sufiicient quantity of an organometallic compound to increase the lubricity of the silicone base lubricant, said compound being a compound of a group IHA-IVA metal and containing a carbon-to-metal bond in the molecule, which method comprises rubbing said surfaces together at low initial loads when in contact with said lubricant and gradually increasing the load between said surfaces up to the operating load.

4. A method for lubricating rubbing surfaces with a lubricant consisting essentially of a silicone base lubricant containing a sufficient quantity of an organometallic compound to increase the lubricity of said silicone base lubricant, said compound containing a group IIIA-IVA metal and a carbon-to-metal bond in the molecule, which method comprises initially injecting between the rubbing surfaces a break-in composition consisting essentially of a mineral oil base lubricant containing an effective amount of an organometallic compound of a group IHA-IVA metal containing a carbon-to-metal bond in the molecule, rubbing said surfaces together in contact with said breakin composition, removing said break-in composition from between the rubbing surfaces, and replacing it with a lubricant composition consisting essentially of a silicone base lubricant having admixed therewith an organometallic compound of a group IHA-IVA metal, containing a carbon-to-metal bond in the molecule, in sufficient quantity to lay down a protective film on the rubbing surfaces.

5. The method of claim 4 wherein a relatively low load is applied between the rubbing surfaces during operation with the break-in lubricant after which said load is gradually increased to the operating load.

6. A method for lubricating essentially non-reactive rubbing surfaces which have a high resistance to corrosion with a lubricant consisting essentially of a silicone base lubricant containing a suflicient quantity of an organornetallic compound to increase the lubricity of the silicone base lubricant, said compound being a compound of a group IIIA-IVA metal and containing a carbon-to-metal bond in the molecule, which method comprises rubbing said surfaces together at low initial loads when in contact with said lubricant and gradually increasing the load between said surfaces up to the operating'load.

7. The method of claim.6 wherein the rubbing surfaces are gold.

3,058,912 1a 14 7 8. The composition of claim 1 wherein said organo- 2,354,218 Murray July 25, 1944 metallic compound is dibutyl tin sulfide. 2,642,395 Currie June 16, 1953 References Cited in the file of this patent OTHER REFERENCES UNITED STATES PATENTS 5 Lubrication, vol. 43, June 1957, N0. 6, pub. by the 2,334,566 Lincoln Nov. 16, 1943 Texas Co., pages 68-72. 

1. COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF A SILICONE BASE LUBRICANT AND AN ORGANOMETALLIC COMPOUND OF A GROUP IIIA-IVA METAL HAVING A CARBON-TO-METAL BOND IN THE MOLECULE, SAID COMPOUND CONTAINING FROM 2 TO 35 CARBON ATOMS PER MOLECULE AND BEING PRESENT IN A QUANTITY SUFFICIENT TO INCREASE THE LUBRICITY OF THE SILICONE BASE LUBRICANT. 